Bollinger Bands are drawn at a given number of standard
deviations from a moving average of a price. Since standard deviation is a
measure of volatility, the bands are self-adjusting: widening during volatile
markets and contracting during calmer periods. Bollinger Bands were created by
John Bollinger.
An Envelope is comprised of two moving averages. One moving
average is shifted upward and the second moving average is shifted downward.
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